I've been blown away by being able to finally, at long last, game on my linux machine. Between emulators and Steam's Proton, I'm rarely if every needing to boot into W$ just for games. That said,while I can play the gamepass web streaming thing, I don't know if there is a way to use gamepass locally with Proton. Is that possible?
It is currently not possible. Games installed through GamePass have some kind of Windows compatibility layer which cannot be run by any wine or proton versions. At least not yet.
Yep, for steamdeck your options are to install windows or to stream. Greenlight is a good linux application that handles the streaming better than the website imo. It can also do remote play if you have an Xbox, which generally has much lower input latency.